It is one of the great mysteries of this Washington Nationals season, capable of stealing your attention, on any given night, from a brewing blockbuster trade, an ace's spoiled debut, a beauty pageant queen and busloads of fans from Philadelphia: What is the deal with Craig Stammen?

Some days, Stammen pitches like fodder just waiting to be replaced if and when Nationals actually get good. On others, like Friday night, he pitches like his presence will be one of the forces that eventually help push the Nationals into contention. Before 32,590 at Nationals Park, Stammen stifled the Philadelphia Phillies for 6 1/3 innings in an 8-1 Nationals victory. The Nationals pummeled Roy Oswalt in his Phillies debut, sending thousands of invading fans to a long drive home on Interstate 95.

With less than 24 hours before the trade deadline, Adam Dunn's future still in doubt and Stephen Strasburg on the disabled list, the Nationals won for the third time in four games against a National League East heavyweight. After Miss Iowa tossed out the first pitch to Miguel Batista, they scored five runs, four earned, in six innings against Oswalt, whom the Phillies acquired Thursday from the Houston Astros. He owned the marquee, but not the game.

"The story," Dunn said, "is Stammen."

The Nationals won, really, because the Good Craig Stammen showed up. Stammen struck out five and allowed one run on five hits and a walk, shutting out the Phillies until Jayson Werth led off the seventh inning with a solo homer, Philadelphia's only run.

"I can't be satisfied, because I've got to be able to do it two, three, four, five, six, seven, eight times in a row," Stammen said. "That's the goal. That's the corner I have to turn to be an effective starter in the big leagues."

On Friday night, Stammen may have showed he is turning a hard-to-define corner. In his last start, despite lasting just five innings in Milwaukee, Stammen felt he had thrown better than any time this season. In his last three starts, he has allowed four earned runs in 17 1/3 innings. Then again, Stammen surrendered 11 earned runs in the 8 2/3 innings before that.

Against the Phillies, he carved up both sides of the plate with his boring sinker and a sharp curveball. He left Ryan Howard shaking his head after he snuck an inside fastball by him. He retired eight in a row at one point. Before Stammen pitched this week, he watched his two starts against the Phillies from the start of the season, when he allowed 11 runs in nine innings. "I owed them one," he said.

Stammen allowed two or fewer earned runs for the seventh time in 13 starts this season. And yet, his ERA stood at 5.24 after the game. The last time he faced the Phillies, back in mid-April, Stammen recorded four outs and yielded seven earned runs. He started the season as the Nationals' third starter, and that's what he is right now, but in between the Nationals demoted him to Class AAA Syracuse. You figure it out.

Stammen received support from a strange beginning. In the third inning, the Nationals already led, 1-0, thanks to Nyjer Morgan's leadoff triple on Oswalt's very first pitch as a Phillie. ("I wanted to get the party started off right," Morgan said.) Oswalt grounded an apparent single through the right side, toward Roger Bernadina, who was shallow in right field. Dunn hung out a few steps away from first.

"If he sees me running straight to the base," Dunn said, "he's going to run hard."

Bernadina and Dunn both knew: They had a chance to retire Oswalt. Bernadina charged, Dunn finally moved to the base. Bernadina fired low to Dunn, who, facing right field, scooped the ball in time to retire Oswalt, 9-3.

In the bottom of the inning, Stammen started a rally with a leadoff single. He moved to second when Oswalt hit Morgan with a pitch. Adam Kennedy followed with a sacrifice bunt, dropping it a foot or two in front of home plate. Catcher Carlos Ruiz pounced on the ball and fired to third -- which, unfortunately for him, had been left unoccupied. The ball sailed into right field, and the Nationals had another run.

And Kennedy had one of his four hits. After struggling to acclimate to a bench role at the start of the year, Kennedy is batting .394 since the all-star break. "It's a grind, you know?" Kennedy said. "But it's part of the job. Hopefully I can end the year with a good feeling."

The Nationals would only add on, the final meaningful blow a bases-loaded, two-run double by Bernadina in the seventh. At the end of the game, a blowout the Nationals let Collin Balester finish off, the crowd stood and cheered. The Phillies fans -- who throughout the night chanted "Let's go, Phillies!" had been drowned out, the trade deadline, at least for a few, fleeting hours, shoved aside.

"As long as we keep winning," Stammen said, "hopefully those chants won't even be heard when the Phillies come to town."

And Stammen had to wonder how he could make things like that happen more often.